Method and apparatus for feedback transmission in wireless communication system

ABSTRACT

A method and an apparatus for feedback transmission in a wireless communication system are provided. A terminal selects at least one subband among plural subbands constituting a set of subbands and transmits information about feedback measured for the at least one subband. The feedback information contains an index of the at least one subband, and the at least one subband is selected in consideration of resource mapping of the plural subbands.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority of U.S. Provisional application No. 61/230,117 filed on Jul. 31, 2009, and Korean Patent application No. 10-2010-0073770 filed on Jul. 30, 2010, all of which are incorporated by reference in their entirety herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to wireless communications and, more particularly, to a method and apparatus for transmitting a feedback in a wireless communication system.

2. Related Art

The institute of electrical and electronics engineers (IEEE) 802.16e standard was adopted in 2007 as a sixth standard for international mobile telecommunication (IMT)-2000 in the name of ‘WMAN-OFDMA TDD’ by the ITU-radio communication sector (ITU-R) which is one of sectors of the international telecommunication union (ITU). An IMT-advanced system has been prepared by the ITU-R as a next generation (i.e., 4^(th) generation) mobile communication standard following the IMT-2000. It was determined by the IEEE 802.16 working group (WG) to conduct the 802.16m project for the purpose of creating an amendment standard of the existing IEEE 802.16e as a standard for the IMT-advanced system. As can be seen in the purpose above, the 802.16m standard has two aspects, that is, continuity from the past (i.e., the amendment of the existing 802.16e standard) and continuity to the future (i.e., the standard for the next generation IMT-advanced system). Therefore, the 802.16m standard needs to satisfy all requirements for the IMT-advanced system while maintaining compatibility with a mobile WiMAX system conforming to the 802.16e standard.

Technology for supporting reliable and high-speed data service may include multiple input multiple output (MIMO). MIMO technology can be used to improve the efficiency of data transmission and reception using multiple transmission antennas and multiple reception antennas. MIMO technology includes spatial multiplexing, transmit diversity, beam-forming and the like. An MIMO channel matrix according to the number of reception antennas and the number of transmission antennas can be decomposed into a number of independent channels. Each of the independent channels is called a layer or stream. The number of layers is called a rank.

A user equipment (UE) may transmit a feedback through uplink. The feedback may include channel information necessary for data transmission. A base station (BS) may schedule radio resources using the feedback received from the UE and transmit data. A closed loop scheme is a scheme of transmitting data by compensating for channel information included in a feedback from UE, and an open loop scheme is a scheme of transmitting data by not compensating for channel information included in a feedback from UE. A feedback may not be transmitted according to the open loop scheme, and a BS may do not use channel information included in a feedback although the channel information is included in the feedback. In general, in a wireless communication system, the open loop scheme may be applied to a channel environment for UE that moves at high speed, and the closed loop scheme may be applied to a channel environment for UE that moves at low speed. The open loop scheme is applied to a channel for UE that moves at high speed because the channel is greatly changed, making channel information, included in a feedback, difficult to be reliable. The closed loop scheme may be applied to a channel environment for UE that moves at low speed because the channel environment is relatively less changed and channel information included in a feedback is reliable and less sensitive to delay.

An uplink control channel may carry various kinds of pieces of feedback information. The pieces of feedback information may include a channel quality indicator (CQI), an MIMO feedback, acknowledgement/non-acknowledgement (ACK/NACK), an uplink synchronization signal, a bandwidth request, etc. The pieces of feedback information may be combined in various ways according to a channel environment or a predetermined configuration and transmitted. Furthermore, feedback information about the entire bandwidth may be measured and fed back and feedback information about some subbands of the bandwidth may be measured and fed back. If feedback information about some subbands is measured, the indices of the relevant subbands may also be fed back.

There has not yet been proposed a detailed method of feeding a subband index back in an IEEE 802.16m system. Accordingly, it is necessary to propose a method of efficiently feeding a subband index back.

SUMMARY OF THE INVENTION

The present invention provides a method and apparatus for transmitting a feedback in a wireless communication system.

In an aspect, a method of transmitting a feedback in a wireless communication system is provided. The method includes selecting at least one subband among a plurality of subbands forming a subband set, and transmitting feedback information measured for the at least one subband, wherein the feedback information comprises an index of the at least one subband, and the at least one subband is selected by taking a frequency partition or a resource mapping of the plurality of subbands into consideration. The at least one subband may be selected from all subband sets, and the at least one subband may belong to a selected specific frequency partition. Information about the specific frequency partition may be signalized by a feedback allocation advanced-MAP (A-MAP) information element (IE). The specific frequency partition may be selected by a user equipment. Information about the specific frequency partition may be fed back to a base station according to a primary fast feedback channel (PFBCH) encoding type 1. The at least one subband may be selected from the subband set belonging to a specific frequency partition. The at least one subband may be selected from all subband sets, and the at least one subband may belong to a subband set mapped in a contiguous logical resource unit (CLRU). The at least one subband may be selected from a subband set mapped in the CLRU. The feedback information may be transmitted to a base station through a PFBCH or a second fast feedback channel (SFBCH).

In another aspect, an apparatus for transmitting a feedback in a wireless communication system is provided. The apparatus includes a radio frequency (RF) unit configured for transmitting feedback information measured for at least one subband, and a processor, coupled to the RF unit, configured for selecting the at least one subband from among a plurality of subbands forming a subband set, wherein the feedback information comprises an index of the at least one subband, and the at least one subband is selected by taking a frequency partition or a resource mapping of the plurality of subbands into consideration. The at least one subband may be selected from all subband sets, and the at least one subband may belong to a selected specific frequency partition. The at least one subband may be selected from the subband set belonging to a specific frequency partition. The at least one subband may be selected from all subband sets, and the at least one subband may belong to a subband set mapped in a contiguous logical resource unit (CLRU). The at least one subband may be selected from a subband set mapped in the CLRU. The feedback information may be transmitted to a base station through a primary fast feedback channel (PFBCH) or a second fast feedback channel (SFBCH).

Since a subband index is fed back by taking the transmission power levels of a bandwidth and a frequency partition and the resource mapping of a subband into consideration, feedback information, such as a channel quality indictor (CQI), can be precisely measured and the subband index can be efficiently fed back.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a wireless communication system.

FIG. 2 shows an example of a frame structure.

FIG. 3 shows an example of an uplink resource structure.

FIG. 4 shows an example of a method of partitioning the entire frequency band into a plurality of frequency partitions.

FIG. 5 shows an example of a cellular system in which the FFR scheme is used.

FIG. 6 shows an example of a subband partitioning process.

FIG. 7 is an exemplary diagram showing a frequency band.

FIG. 8 shows an example of uplink resources used in the PFBCH.

FIG. 9 is a block diagram showing a process in which feedback information is mapped to a PFBCH.

FIG. 10 is a block diagram showing a process in which feedback information is mapped to an SFBCH.

FIG. 11 is an embodiment of the proposed feedback transmission method.

FIG. 12 is a block diagram showing a BS and UE in which the embodiments of the present invention are implemented.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

A technology below can be used in a variety of wireless communication systems, such as code division multiple access (CDMA), frequency division multiple access (FDMA), time division multiple access (TDMA), orthogonal frequency division multiple access (OFDMA), and single carrier frequency division multiple access (SC-FDMA). CDMA can be implemented using radio technology, such as universal terrestrial radio access (UTRA) or CDMA2000. TDMA can be implemented using radio technology, such as global system for mobile communications (GSM)/general packet radio service (GPRS)/enhanced data rates for GSM evolution (EDGE). OFDMA can be implemented using radio technology, such as IEEE 802.11(Wi-Fi), IEEE 802.16(WiMAX), IEEE 802-20, or Evolved UTRA (E-UTRA). IEEE 802.16m is the evolution of IEEE 802.16e, and it provides a backward compatibility with an IEEE 802.16e-based system. UTRA is part of a universal mobile telecommunications system (UMTS). 3rd generation partnership project (3GPP) long term evolution (LTE) is part of evolved UMTS (E-UMTS) using evolved-UMTS terrestrial radio access (E-UTRA), and it adopts OFDMA in downlink (DL) and SC-FDMA in uplink (UL). LTE-A (advanced) is the evolution of 3GPP LTE.

IEEE 802.16m is chiefly described as an example in order to clarify the description, but the technical spirit of the present invention is not limited to IEEE 802.16m.

FIG. 1 shows a wireless communication system.

Referring to FIG. 1, the wireless communication system 10 includes one or more base stations (BSs) 11. The BSs 11 provide communication services to respective geographical areas (in general called ‘cells’) 15 a, 15 b, and 15 c. Each of the cells can be divided into a number of areas (called ‘sectors’). A user equipment (UE) 12 can be fixed or mobile and may be referred to as another terminology, such as a mobile station (MS), a mobile terminal (MT), a user terminal (UT), a subscriber station (SS), a wireless device, a personal digital assistant (PDA), a wireless modem, or a handheld device. In general, the BS 11 refers to a fixed station that communicates with the UEs 12, and it may be referred to as another terminology, such as an evolved-NodeB (eNB), a base transceiver system (BTS), or an access point.

The UE belongs to one cell. A cell to which a UE belongs is called a serving cell. A BS providing the serving cell with communication services is called a serving BS. A wireless communication system is a cellular system, and so it includes other cells neighboring a serving cell. Other cells neighboring the serving cell are called neighbor cells. A BS providing the neighbor cells with communication services is called as a neighbor BS. The serving cell and the neighbor cells are relatively determined on the basis of a UE.

This technology can be used in the downlink (DL) or the uplink (UL). In general, DL refers to communication from the BS 11 to the UE 12, and UL refers to communication from the UE 12 to the BS 11. In the DL, a transmitter may be part of the BS 11 and a receiver may be part of the UE 12. In the UL, a transmitter may be part of the UE 12 and a receiver may be part of the BS 11.

FIG. 2 shows an example of a frame structure.

Referring to FIG. 2, a superframe (SF) includes a superframe header (SFH) and four frames F0, F1, F2, and F3. Each frame may have the same length in the SF. Although it is shown that each SF has a length of 20 milliseconds (ms) and each frame has a length of 5 ms, the present invention is not limited thereto. A length of the SF, the number of frames included in the SF, the number of SFs included in the frame, or the like can change variously. The number of SFs included in the frame may change variously according to a channel bandwidth and a cyclic prefix (CP) length.

One frame includes 8 subframes SF0, SF1, SF2, SF3, SF4, SFS, SF6, and SF7. Each subframe can be used for uplink or downlink transmission. One subframe includes a plurality of orthogonal frequency division multiplexing (OFDM) symbols in a time domain, and includes a plurality of subcarriers in a frequency domain. An OFDM symbol is for representing one symbol period, and can be referred to as other terminologies such as an OFDM symbol, an SC-FDMA symbol, etc., according to a multiple access scheme. The subframe can consist of 5, 6, 7, or 9 OFDMA symbols. However, this is for exemplary purposes only, and thus the number of OFDMA symbols included in the subframe is not limited thereto. The number of OFDMA symbols included in the subframe may change variously according to a channel bandwidth and a CP length. A subframe type may be defined according to the number of OFDMA symbols included in the subframe. For example, it can be defined such that a type-1 subframe includes 6 OFDMA symbols, a type-2 subframe includes 7 OFDMA symbols, a type-3 subframe includes 5 OFDMA symbols, and a type-4 subframe includes 9 OFDMA symbols. One frame may include subframes each having the same type. Alternatively, one frame may include subframes each having a different type. That is, the number of OFDMA symbols included in each subframe may be identical or different in one frame. Alternatively, the number of OFDMA symbols included in at least one subframe of one frame may be different from the number of OFDMA symbols of the remaining subframes of the frame.

Time division duplex (TDD) or frequency division duplex (FDD) may be applied to the frame. In the TDD, each subframe is used in uplink or downlink transmission at the same frequency and at a different time. That is, subframes included in a TDD frame are divided into an uplink subframe and a downlink subframe in the time domain. A switching point refers to a point where a transmission direction is changed from an uplink region to a downlink region or from a downlink region to an uplink region. In the TDD, the number of the switching points in each frame may be two. In the FDD, each subframe is used in uplink or downlink transmission at the same time and at a different frequency. That is, subframes included in an FDD frame are divided into an uplink subframe and a downlink subframe in the frequency domain. Uplink transmission and downlink transmission occupy different frequency bands and can be simultaneously performed.

A superframe header (SFH) may carry an essential system parameter and system configuration information. The SFH may be located in a first subframe of a superframe. The SFH may occupy last 5 OFDMA symbols of the first subframe. The SFH can be classified into a primary-SFH (P-SFH) and a secondary-SFH (S-SFH). The P-SFH and the S-SFH may be transmitted in every superframe. The S-SFH may be transmitted in two consecutive superframes. Information transmitted on the S-SFH may be classified into three sub-packets, i.e., an S-SFH SP1, an S-SFH SP2, and an S-SFH SP3. Each sub-packet can be transmitted periodically with a different period. Information transmitted in the S-SFH SP1, the S-SFH SP2, and the S-SFH SP3 may have different importance from one another. The S-SFH SP1 may be transmitted with a shortest period, and the S-SFH SP3 may be transmitted with a longest period. The S-SFH SP1 includes information on network re-entry. The S-SFH SP2 includes information on initial network entry and network discovery. The S-SFH SP3 includes other important system information.

FIG. 3 shows an example of an uplink resource structure.

Referring to FIG. 3, an uplink subframe can be divided into at least one frequency partition (FP). Herein, the subframe is divided into two FPs (i.e., FP1 and FP2) for example. However, the number of FPs in the subframe is not limited thereto. The number of FPs can be 4 at most. Each FP consists of at least one physical resource unit (PRU) across all available OFDMA symbols in a subframe. In addition, Each FP may include contiguous/localized PRUs and/or distributed PRUs. Each FP can be used for other purposes such as fractional frequency reuse (FFR). In FIG. 3, the second FP (i.e., FP2) includes the distributed resource allocation and the contiguous resource allocation. ‘Sc’ denotes a subcarrier.

The PRU is a basic physical unit for resource allocation. The PRU consists of a Psc consecutive subcarriers and Nsym consecutive OFDMA symbols. Nsym may be equal to the number of OFDMA symbols included in one subframe. Therefore, Nsym can be determined according to a subframe type. For example, when one subframe consists of 6 OFDMA symbols, the PRU may be defined with 18 subcarriers and 6 OFDMA symbols.

A logical resource unit (LRU) is a basic logical unit for distributed resource allocation and contiguous resource allocation. The LRU consists of a Psc consecutive subcarriers and Nsym consecutive OFDMA symbols. A size of a LRU for transmitting a control channel is equal to a size of a LRU for transmitting data. A plurality of users may share one control LRU. Also, the LRU may include pilot. Therefore, a desired number of subcarriers for one LRU depends on the number of allocated pilots and the existence of control channel.

A distributed logical resource unit (DLRU) may be used to obtain a frequency diversity gain. The DLRU includes a subcarrier group distributed in a resource region in one frequency partition. The DLRU has the same size as the PRU. A minimum unit for consisting the DLRU may be a tile. A size of an uplink tile is 6 subcarriers×Nsym OFDMA symbols. Nsym may be changed according to a subframe type.

A contiguous logical resource unit (CLRU) may be used to obtain a frequency selective scheduling gain. The CLRU includes a subcarrier group contiguous in a resource region. The CLRU has the same size as the PRU.

Meanwhile, in a cellular system where multiple cells exist, a fractional frequency reuse (FFR) scheme may be used. The FFR scheme is a scheme for partitioning the entire frequency band into a plurality of frequency partitions (FPs) and allocating the frequency partition to each cell. According to the FFR scheme, different frequency partitions may be allocated to neighboring cells and the same frequency partition may be allocated to cells which are distant from one another. Accordingly, inter-cell interference (ICI) can be reduced, and the performance of cell edge UE can be increased.

FIG. 4 shows an example of a method of partitioning the entire frequency band into a plurality of frequency partitions.

Referring to FIG. 4, the entire frequency band is partitioned into a first frequency partition FP0, a second frequency partition FP1, a third frequency partition FP2, and a fourth frequency partition FP3. Each of the frequency partitions may be logically and/or physically from the entire frequency band.

FIG. 5 shows an example of a cellular system in which the FFR scheme is used.

Referring to FIG. 5, each cell is divided into an inner cell and a cell edge. Furthermore, each cell is divided into 3 sectors. The entire frequency band is partitioned into 4 frequency partitions FP0, FP1, FP2, and FP3.

The first frequency partitions FP0 are allocated to the inner cell. Any one of the second frequency partition FP1 to the fourth frequency partition FP3 is allocated to each the sectors of the cell edge. Here, different frequency partitions are allocated to neighboring cells. Hereinafter, an allocated frequency partition is called an active frequency partition, and a non-allocated frequency partition is called an inactive frequency partition. For example, if the second frequency partition FP1 is allocated, the second frequency partition is an active frequency partition and the third frequency partition FP2 and the fourth frequency partition FP3 become inactive frequency partitions.

A frequency reuse factor (FRF) may be defined according to how many the entire frequency band can be partitioned into cells (or sectors). In this case, the FRF of the inner cell may be 1, and the FRF of each sector of the cell edge may be 3.

When a plurality of cells exists, uplink resources may be mapped through processes, such as a subband partitioning, a miniband permutation, and a frequency partitioning.

FIG. 6 shows an example of a subband partitioning process. FIG. 6 shows the subband partitioning process in case of 10 MHz bandwidths.

A plurality of PRUs is allocated in a subband (SB) and a miniband (MB). The subband includes N1 contiguous PRU, and the miniband includes N2 contiguous PRUs. N1 may be 4, and N2 may be 1. The subband is suitable for frequency selective resource allocation because PRUs contiguous in the frequency domain are allocated to the subband. The miniband is suitable for frequency distributed resource allocation and may be subject to permutation in the frequency domain.

The number of subbands may be indicated by K_(SB). The number of PRUs allocated to the subband may be indicated by L_(SB), and L_(SB)=N1*K_(SB). K_(SB) may vary according to the bandwidth. K_(SB) may be determined by an uplink subband allocation count (USAC). The length of the USAC may be 3 bits to 5 bits and may be broadcasted through an SFH, etc. The remaining PRUs remained after being allocated to the subband are allocated to the miniband. The number of minibands may be indicated by K_(MB). The number of PRUs allocated to the miniband may be indicated by L_(MB), and L_(MB)=N2*K_(MB). The maximum number of subbands that may be formed in the resource region is N_(sub)=└N_(PRU)/N1┘, the total number of PRUs N_(PRU)=L_(SB)+L_(MB).

A plurality of PRUs is divided into a subband and a miniband and rearranged within a subband PRU PRU_(SB) and a miniband PRU PRU_(MB). Each of the PRUs within the PRU_(SB) is indexed to any one of 0 to (L_(SB)−1), and each of the PRUs within the PRU_(MB) is indexed to any one of 0 to (L_(MB)−1). Furthermore, in a miniband permutation process, the PRU_(MB) is mapped to a permutation PRU PPRU_(MB). In the frequency partitioning process, the PRUs of the PRU_(SB) and the PPRU_(MB) are allocated to at least one frequency partition.

FIG. 7 is an exemplary diagram showing a frequency band.

The entire frequency band is divided into a plurality of subbands (SBs). In ‘SBn’ indicating the subband, n indicates the index of each subband. In FIG. 7, the entire bandwidth is divided into 12 subbands, but not limited thereto. All the bands may be divided into 12 or lower or higher subbands.

Meanwhile, a best-M scheme means that M specific subbands are selected from among a plurality of subbands. For example, M subbands having the best channel state may be selected. The best band means the selected M subbands. The remaining bands are the remaining subbands other than the best band, from all the bands. For example, in FIG. 7, subband 3, 6 and 11 are selected the best bands according to a best-3 scheme.

Hereafter, a control channel used for transmitting a control signal or a feedback signal is described. The control channel may be used for transmission of various kinds of control signals for communication between a base station and a user equipment. The control channel described below may be applied to an uplink control channel and a downlink control channel.

The control channel is designed by taking the following points into consideration.

(1) A plurality of tiles included in a control channel can be distributed over the time domain or the frequency domain in order to obtain a frequency diversity gain. For example, assuming that a DRU includes three tiles each including six consecutive subcarriers on six OFDM symbols, the control channel includes the three tiles, and each of the tiles can be distributed over the frequency domain or the time domain. In some embodiments, the control channel can include at least one tile including a plurality of mini-tiles, and the plurality of mini-tiles can be distributed over the frequency domain or the time domain. For example, the mini-tile can consist of (OFDM symbols×subcarriers)=6×6, 3×6, 2×6, 1×6, 6×3, 6×2, 6×1 or the like. Assuming that a control channel, including (OFDM symbols×subcarriers) of IEEE 802.16e=the tiles of a 3×4 PUSC structure, and a control channel, including mini-tiles, are multiplexed through a Frequency Division Multiplexing (FDM) method, the mini-tiles can consist of (OFDM symbols×subcarriers)=6×2, 6×1, etc. When taking only the control channel, including the mini-tiles, into consideration, the mini-tiles can consist of (OFDM symbols×subcarriers)=6×2, 3×6, 2×6, 1×6 or the like.

(2) To support a high-speed mobile station, the number of OFDM symbols constituting a control channel must be a minimum. For example, in order to support a mobile station moving at the speed of 350 km/h, the number of OFDM symbols constituting a control channel is properly 3 or less.

(3) The transmission power of a mobile station per symbol is limited. To increase the transmission power of a mobile station per symbol, it is advantageous to increase the number of OFDM symbols constituting a control channel. Accordingly, a proper number of OFDM symbols has to be determined with consideration taken of (2) a high-speed mobile station and (3) the transmission power of a mobile station per symbol.

(4) For coherent detection, pilot subcarriers for channel estimation have to be uniformly distributed over the time domain or the frequency domain. The coherent detection method is used to perform channel estimation using a pilot and then find data loaded on data subcarriers. For the power boosting of pilot subcarriers, the number of pilots per OFDM symbol of a control channel has to be identical in order to maintain the same transmission power per symbol.

(5) For non-coherent detection, a control signal has to consist of orthogonal codes/sequences or semi-orthogonal codes/sequences or has to be spread.

Uplink control channels may include a fast feedback channel (FFBCH), a hybrid automatic repeat request (HARD) feedback channel (HFBCH), a ranging channel, a bandwidth request channel (BRCH), and so on. Information, such as a CQI, an MIMO feedback, ACK/NACK, an uplink synchronization signal, and a bandwidth request, may be transmitted through the uplink control channel. The FFBCH, the HFBCH, the ranging channel, the BRCH, etc. may be located in any place of an uplink subframe or a frame.

The uplink control channel may be allocated through downlink control information that is transmitted from a BS through downlink. The downlink control information may be broadcast to all the UEs or may be transmitted to each UE in unicast service. The P-SFH or the S-SFH mentioned above is a broadcast downlink control signal, and a plurality of advanced-MAP information elements (A-MAP IEs) may be defined as basic elements of unicast service control.

A feedback allocation A-MAP IE for the dynamic allocation or release of a feedback channel, from among the plurality of A-MAP IEs, may be transmitted to UE. Feedback channels that may be allocated or released by the feedback allocation A-MAP IE include a PFBCH and an SFBCH. If feedback channels already allocated to UE for a downlink carrier exist and new feedback channels for the relevant downlink carrier are allocated again, the original feedback channels may be automatically released.

Table 1 is an example of a feedback allocation A-MAP IE for the allocation of feedback channels.

TABLE 1 Size in Syntax bits Description/Notes Feedback-Allocation-MAP_IE( ) — — { A-MAP IE Type [4] Feedback Allocation A-MAP IE = 0b0010 Channel Index Variable Feedback channel index within the UL fast feedback control resource region Short-term Feedback Period (p) [3] A feedback is transmitted on the FBCH every 2^(p) frames Long-term Feedback Period (q) [2] A long-term feedback is transmitted on the FBCH every 2^(q) short-term feedback opportunity If q = 0b00, long-term feedback is not used. Frame offset [3] The AMS starts reporting at the frame of which the number has the same 3 LSB as the specified frame offset. If the current frame is specified, the AMS should start reporting in eight frames Allocation Duration(d) [3] A FBCH is transmitted on the FBCH channels indexed by Channel Index for 8 * 2^(d) frames. If d = 0b000, the FBCH is deallocated. If d = 0b111, the AMS should report until the ABS command for the AMS to stop. ACK Allocation Flag [1] Indicate if one ACK channel is allocated If (ACK Allocation Flag == 0b1){ HFA [3] HARQ feedback channel allocation for Feedback Channel De- allocation confirmation } MaxMt Variable Variable number of bits - depends on number of transmit [1-2] antenna Nt If Nt = 2 (SU-MIMO and MU-MIMO): 0b0: 1, 0b1: 2 If Nt = 4 (SU-MIMO and MU-MIMO): 0b00: 1, 0b01: 2, 0b10: 3, 0b11: 4 If Nt = 8 (SU-MIMO): 0b000: 1, 0b001: 2, 0b011: 4, 0b111: 8 If Nt = 8 ÷ (MU-MIMO): 0b00: 1, 0b01: 2, 0b10: 3, 0b11: 4 MFM [3] MIMO Feedback Mode as defined in Table 691 If (MFM = 2, 3, 5, 6) {  Feedback Format [2] } If(MFM=0,1,4,7){  FPI [2] Frequency partition indication: ABS indicate AMS to send wideband CQI and STC rate of the frequency partition and reuse factor in the future: 0b00: Frequency partition index 0 0b01: Frequency partition index 1 0b10: Frequency partition index 2 0b11: Frequency partition index 3 } If (MFM = 0,1 & Long-term Feedback Period != 0b00) {  Long term FPI [2] Frequency partition indication: ABS indicate AMS to send wideband CQI and STC rate for the second frequency partition using long term feedback: 0b00: Frequency partition index 0 0b01: Frequency partition index 1 0b10: Frequency partition index 2 0b11: Frequency partition index 3 } If (MFM == 3,4,6,7) { CL SU and MU MIMO  CM [2] Codebook Feedback Mode and Codebook Coordination Enable 0b00: standard with CCE disabled 0b01: adaptive with CCE disabled 0b10: differential with CCE disabled 0b11: standard with CCE enabled  CS [1] Codebook subset } If(MFM=0, 1, 5){  Measurement Method [1] 0b0: Use the midamble for CQI measurements  Indication 0b1: Use pilots in OL region with MaxMt streams for CQI measurements } Padding Variable Padding to reach byte boundary MCRC [16]  16 bit CRC masked by Station ID } — —

The definition of fields forming the feedback allocation A-MAP IE of Table 1 is as follows.

Channel index: define an index on the uplink resources of a feedback channel on which UE transmits feedback information. Here, a 1 to 1 relationship is set up between the relevant UE and the channel index. That is, feedback channels allocated to UEs do not overlap with each other.

Short-term feedback period: define the period where short-term feedback information that is varied relatively frequently according to a channel environment, from among pieces of feedback information, is transmitted. The short-term feedback information may include a CQI, a precoding matrix indicator (PMI), etc. The short-term feedback information is transmitted every 2^(p) frames according to the short-term feedback period.

Long-term feedback period: define the period where long-term feedback information that is not varied frequently, from among pieces of feedback information, is transmitted. The long-term feedback information may include a subband index, an MIMO feedback mode, etc. The long-term feedback information is transmitted every 2^(q) frames according to the long-term feedback period, and the long-term feedback information is not transmitted when q=0.

Allocation duration: define the allocation duration of a feedback channel. Assuming that the value of a field indicating the allocation duration is d, feedback channels are allocated as much as 8×2^(d) frames. When d=0b000, the feedback channels are released. When d=0b111, the feedback channels remain continued until a release command is received from a BS.

ACK allocation flag: A field for allocating an ACK channel on which a message to check the release of a feedback channel is transmitted. When d indicating the allocation duration is d=0b000, the value of the ACK allocation flag is 0b1. If the channel index of a feedback channel newly allocated is identical with the channel index of a released feedback channel even when d is not d=0b000, the value of the ACK allocation flag is set to 0b1.

MIMO feedback mode (MFM): define an MIMO feedback mode, and the MFM may be defined by Table 2 to be described later.

Feedback format: define a feedback format index when feedback information is transmitted through a feedback channel. The feedback format index may indicate a type of feedback information, etc. Feedback formats according to different MIMO feedback modes may be defined by Tables 3 to 7 to be described later.

frequency partition indication (FPI): indicate information about a frequency partition that measures feedback information to be transmitted in the short-term feedback period. When the number of frequency partitions is 1, the FPI field may do not exist.

Long-term FPI: indicate information about another frequency partition that measures feedback information to be transmitted in the long-term feedback period. When the number of frequency partitions is 1, the long-term FPI field does not exist, and when the number of frequency partitions is 2, it is implicitly signalized by the FPI field.

codebook mode (CM): indicate a codebook feedback mode.

measurement method indication: indicate a midamble or a pilot for CQI measurement.

The MIMO feedback mode may support MIMO transmission. When a BS allocates feedback channels, the BS informs UE of an MIMO feedback mode, and the UE transmits feedback information according to the MIMO feedback mode. Table 2 is an example of MIMO feedback modes and MIMO transmission modes supported according to the MIMO feedback modes.

TABLE 2 Feedback Supported MIMO Mode Description Feedback contents Type of RU transmission mode Mode 0 OL SU MIMO 1. STC Rate Diversity(DRU, MIMO mode 0 and SFBC/SM 2. Wideband CQI Mini-band based MIMO mode 1. (Diversity) CRU) Flexible adaptation between the two modes STC Rate = 1: SFBC CQI STC Rate 2: SM CQI In DRU: Mt = 2 for SM.In Miniband based CRU: Mt >= 2 for SM Mode 1 OL SUMIMO 1. STC Rate Diversity(Mini-band MIMO mode 1 SM (Diversity) 2. Wideband CQI based CRU) Mode 2 OL SUMIMO 1. STC Rate Localized (Subband MIMO mode 1 SM (localized) 2. Subband CQI based CRU, Mini- 3. Subband Selection band based CRU) Mode 3 CL SU MIMO 1. STC Rate Localized (Subband MIMO mode 2 (localized) 2. Subband CQI based CRU, Mini- 3. Subband PMI band based CRU) 4. Subband selection [5. Wideband PMI] 6. Wideband correlation Matrix Mode 4 CL SU MIMO 1. Wideband CQI Diversity(Mini-band MIMO mode 2 (Mt = 1) (Diversity) [2. Wideband PMI] based CRU) 3. Wideband correlation Matrix Mode 5 OL MU 1. Subband CQI Localized (Subband MIMO mode 3 MIMO 2. Subband Selection based CRU, Mini- (localized) 3. Stream indicator band based CRU) Mode 6 CL MU 1. Subband CQI Localized (Subband MIMO mode 4 MIMO 2. Subband PMI based CRU, Mini- (localized) 3. Subband Selection band based CRU) [4. Wideband PMI] 5. Wideband correlation Matrix Mode 7 CL MU 1. Wideband CQI Diversity (Mini- MIMO mode 4 MIMO [2. Wideband PMI] band based CRU) (Diversity) 3. Wideband correlation Matrix

Referring to Table 2, a supported MIMO transmission mode differs according to each MIMO feedback mode. For example, the MIMO feedback mode 0 supports the application of an open loop-single user (OL-SU) MIMO space-frequency block code (SFBC) and spatial multiplexing (SM) within diversity permutation. UE measures a wideband CQI for an SFBC and SM and reports a CQI and a space time coding (STC) rate to a BS. The MIMO feedback mode 3 supports a closed loop-single user (CL-SU) MIMO environment within localized permutation for frequency selective scheduling. The MIMO feedback mode 5 supports an open loop-multi user (OL-MU) MIMO environment within localized permutation for frequency selective scheduling. The MIMO feedback mode 7 supports a closed loop-multi user (CL-MU) MIMO environment within diversity permutation using wideband beamforming.

An FFBCH carries the feedbacks of a CQI and/or MIMO information, and it may be divided two types; a primary fast feedback channel (PFBCH) and a secondary fast feedback channel (SFBCH). The PFBCH carries information of 4 to 6 bits and provides a wideband CQI and/or MIMO feedback. The SFBCH carries information of up to 24 bits and provides a narrowband CQI and/or MIMO feedback. The SFBCH can support more control information bits by using a higher code rate. The PFBCH supports non-coherent detection not using a pilot, and the SFBCH supports coherent detection using a pilot. The FFBCH is started at a predetermined position, and the size of the FFBCH may be defined by a downlink control signal. The FFBCH may be periodically allocated. The number of FFBCHs allocated to UE by a BS may be 1 or lower.

A feedback format defines a type of feedback information transmitted by an FFBCH. The feedback format may be differently defined according to an MIMO feedback mode. That is, feedback information may be differently configured according to the MIMO feedback mode, and the period where the relevant feedback information is transmitted may be differently set.

Table 3 is an example of feedback formats when the MIMO feedback mode is any one of 0, 1, 4, and 7.

TABLE 3 Size in MFM FBCH # reports Feedback Fields bits Description/Notes 0 PFBCH 2 Short Wideband CQI N/A Joint encoding of CQI and and STC rate STC rate Encoding type 0 Long Wideband CQI N/A Joint encoding of CQI and and STC rate STC rate Encoding type 0 Long term FPI for FFR 1 PFBCH 2 Short Wideband CQI N/A Joint encoding of CQI and and STC rate STC rate Encoding type 0 Long Wideband CQI N/A Joint encoding of CQI and and STC rate STC rate Encoding type 0 Long term FPI for FFR 4 PFBCH 2 Short Wideband CQI N/A STC rate = 1 Encoding type 0 Long Wideband PMI N/A PMI for rank 1 Encoding type 2 7 PFBCH 2 Short Wideband CQI N/A STC rate = 1 Encoding type 0 Long Wideband PMI N/A PMI for rank 1 Encoding type 2

When the MIMO feedback mode is 0, 1, 4, or 7, feedback information about the entire measured wideband is transmitted. Here, a PFBCH is used as a feedback channel for carrying the feedback information. A wideband CQI and an STC rate may be transmitted every frame without long-term feedback information or a wideband PMI may be transmitted as long-term feedback information.

Table 4 is an example of feedback formats when the MIMO feedback mode is 2.

TABLE 4 Feedback Size in Format FBCH # reports Feedback Fields bits Description/Notes 0 (M = 1) PFBCH 2 Short Subband CQI N/A Joint encoding of CQI and and STC rate with STC rate (rate = 1 PFBCH and 2) PFBCH encoding Type 0 Long Subband index N/A PFBCH encoding Type 1 1 (M = 1) SFBCH 1 Subband index 3, 4, or 5 Subband index for 5, 10, Subband CQI 4 or 20 MHz STC rate 1~3 Support of STC rate 1 to 8 PFBCH indicator 1 2 (M = 3) SFBCH 2 Short Subband avg 4 Subband index for 5, 10, CQI 2 × 3 = 6 or 20 MHz differential CQI Long Subband index 5, 8 or 11 Wideband STC 1~3 rate PFBCH 1 indicator 3 (M = 5) SFBCH 2 Short Subband avg 4 CQI 2 × 5 = differential CQI 10 Long Subband index 3, 10, or 16 Wideband STC 1~3 rate PFBCH 1 indicator

The MIMO feedback mode 2 supports open loop MIMO. Here, narrowband feedback information is transmitted. That is, the feedback information may be measured in selected 1, 3, or 5 subbands (M in Table 4) and transmitted through a PFBCH or an SFBCH. The feedback information is transmitted through the PFBCH when M=1 and is transmitted through the SFBCH when M=3 or 5. A CQI in a selected subband is transmitted as short-term feedback information, and a subband index is transmitted as long-term feedback information.

Table 5 is an example of feedback formats when the MIMO feedback mode is 3.

TABLE 5 Feedback Description/ Format FBCH # reports Feedback Fields Size in bits Notes 0 (M = 1) PFBCH 3 Short Subband CQI N/A PFBCH encoding Type 0 Short Subband PMI N/A PFBCH encoding Type 2 Long Subband index N/A PFBCH encoding Type 1 1 SFBCH 2 Short Subband differential CQI 2 × 2 Subband index (M = 2) Subband PMI (3~6) × 2 for 5, 10, or Long Subband index 4, 7 or 9 20 MHz Wideband STC rate 1~3 Subband avg CQI 4 PFBCH indicator 1 2 SFBCH 2 Short Subband differential CQI 2 × 3 (M = 3) subband PMI (3~6) × 3 Long Subband index 5, 8 or 11 Wideband STC rate 1~3 Subband avg CQI 4 PFBCH indicator 1 3 SFBCH 2 Short Subband differential CQI 2 × 4 (M = 4) Subband PMI (3~4) × 4 Long Subband index 4, 9 or 14 Wideband STC rate 1~3 Subband avg CQI 4 PFBCH indicator 1

The MIMO feedback mode 3 supports closed loop MIMO, and narrowband feedback information like the MIMO feedback mode 2 is transmitted. Here, a PMI in a selected subband other than a CQI in a selected subband may also be transmitted.

Table 6 is an example of feedback formats when the MIMO feedback mode is 5.

TABLE 6 Feedback Description/ Format FBCH # Reports Feedback Fields Size in bits Notes 0 (M = 1) SFBCH 1 Short Subband index 3, 4, or 5 Subband index for Subband CQI 4 5, 10, or 20 MHz Stream Index 1~2 PFBCH indicator 1 1 (M = 2) SFBCH 2 Short Subband avg_CQI 4 Subband differential 2 × 2 = 4 CQI Stream Index (1~2) × 2 Long Subband index 4, 7, or 9 Subband index for PFBCH indicator 1 5, 10, or 20 MHz 2 (M = 3) SFBCH 2 Short Subband avg_CQI 4 Subband differential 2 × 3 = 6 CQI Stream Index 3 × (1~2) Long Subband index 5, 8, or 11 Subband index for PFBCH indicator 1 5, 10, or 20 MHz 3 (M = 5) SFBCH 3 Short Subband avg_CQI 4 Subband differential 2 × 5 = 10 CQI Stream Index (1~2) × 5 Long Subband index 3, 10, or 16 Subband index for PFBCH indicator 1 5, 10, or 20 MHz

Table 7 is an example of feedback formats when the MIMO feedback mode is 6.

TABLE 7 Feedback Description/ Format FBCH # reports Feedback Fields Size in bits Notes 0 (M = 1) PFBCH 3 Short Subband CQI N/A PFBCH encoding Type 0 Short Subband PMI N/A PFBCH encoding Type 2 Long Subband index N/A PFBCH encoding Type 1 1 (M = 2) SFBCH 2 Short Subband avg_CQI 4 Subband 2 × 2 = 4 differential CQI Stream Index (1~2) × 2 Long Subband index 4, 7, or 9 Subband index for 5, PFBCH indicator 1 10, or 20 MHz 2 (M = 3) SFBCH 2 Short Subband avg_CQI 4 Subband 2 × 3 = 6 differential CQI Stream Index 3 × (1~2) Long Subband index 5, 8, or 11 Subband index for 5, PFBCH indicator 1 10, or 20 MHz 3 (M = 5) SFBCH 3 Short Subband avg_CQI 4 Subband 2 × 5 = 10 differential CQI Stream Index (1~2) × 5 Long Subband index 3, 10, or 16 Subband index for 5, PFBCH indicator 1 10, or 20 MHz

FIG. 8 shows an example of uplink resources used in the PFBCH. The PFBCH may include 3 distributed uplink feedback mini-tiles (FMTs). The FMT may be defined by 2 contiguous subcarriers and 6 OFDM symbols. One resource unit, including 18 subcarriers and 6 OFDM symbols, may include 3 FFBCHs.

FIG. 9 is a block diagram showing a process in which feedback information is mapped to a PFBCH. At step S50, a PFBCH sequence is generated using a PFBCH payload. The PFBCH sequence may be selected from a predetermined PFBCH sequence set. Table 8 is an example of a PFBCH sequence set.

TABLE 8 Index Sequence 0 111111111111 1 101111010110 2 011010111101 3 001010010100 4 101010101010 5 111010000011 6 001111101000 7 011111000001 8 110011001100 9 100011100101 10 010110001110 11 000110100111 12 100110011001 13 110110110000 14 000011011011 15 010011110010 16 101011111100 17 111011010101 18 001110111110 19 011110010111 20 111110101001 21 101110000000 22 011011101011 23 001011000010 24 100111001111 25 110111100110 26 000010001101 27 010010100100 28 110010011010 29 100010110011 30 010111011000 31 000111110001 32 101011001001 33 111011100000 34 001110001011 35 011110100010 36 100111111010 37 110111010011 38 000010111000 39 010010010001 40 111110011100 41 101110110101 42 011011011110 43 001011110111 44 101010011111 45 111010110110 46 001111011101 47 011111110100 48 111111001010 49 101111100011 50 011010001000 51 001010100001 52 110010101111 53 100010000110 54 010111101101 55 000111000100 56 100110101100 57 110110000101 58 000011101110 59 010011000111 60 110011111001 61 100011010000 62 010110111011 63 000110010010

At step S51, the generated PFBCH sequence is modulated, repeated, and mapped to an uplink PFBCH symbol s[k]. Here, 0 of the PFBCH sequence may be mapped to 1, and 1 thereof may be mapped to −1. At step S52, the uplink PFBCH symbol s[k] is mapped to the subcarriers of an FMT.

In transmitting a PFBCH, 4 encoding types may be defined. Encoding types corresponding to the MIMO feedback modes defined in the feedback allocation A-MAP IE and feedback formats may be used. An index value of 6 bits, corresponding to feedback information defined within each encoding type, may be transmitted through the PFBCH.

Table 9 is an example of the PFBCH encoding type 0.

TABLE 9 Index Content (Value) Description/Notes 0 STC rate = 1, MCS = 0000 1 STC rate = 1, MCS = 0001 2 STC rate = 1, MCS = 0010 3 STC rate = 1, MCS = 0011 4 STC rate = 1, MCS = 0100 5 STC rate = 1, MCS = 0101 6 STC rate = 1, MCS = 0110 7 STC rate = 1, MCS = 0111 8 STC rate = 1, MCS = 1000 9 STC rate = 1, MCS = 1001 10 STC rate = 1, MCS = 1010 11 STC rate = 1, MCS = 1011 12 STC rate = 1, MCS = 1100 13 STC rate = 1, MCS = 1101 14 STC rate = 1, MCS = 1110 15 STC rate = 1, MCS = 1111 16 STC rate = 2, MCS = 0000 17 STC rate = 2, MCS = 0001 18 STC rate = 2, MCS = 0010 19 STC rate = 2, MCS = 0011 20 STC rate = 2, MCS = 0100 21 STC rate = 2, MCS = 0101 22 STC rate = 2, MCS = 0110 23 STC rate = 2, MCS = 0111 24 STC rate = 2, MCS = 1000 25 STC rate = 2, MCS = 1001 26 STC rate = 2, MCS = 1010 27 STC rate = 2, MCS = 1011 28 STC rate = 2, MCS = 1100 29 STC rate = 2, MCS = 1101 30 STC rate = 2, MCS = 1110 31 STC rate = 2, MCS = 1111 32 STC rate = 3, MCS = 0100 33 STC rate = 3, MCS = 0101 34 STC rate = 3, MCS = 0110 35 STC rate = 3, MCS = 0111 36 STC rate = 3, MCS = 1000 37 STC rate = 3, MCS = 1001 38 STC rate = 3, MCS = 1010 39 STC rate = 3, MCS = 1011 40 STC rate = 3, MCS = 1100 41 STC rate = 3, MCS = 1101 42 STC rate = 3, MCS = 1110 43 STC rate = 3, MCS = 1111 44 STC rate = 4, MCS = 1000 45 STC rate = 4, MCS = 1001 46 STC rate = 4, MCS = 1010 47 STC rate = 4, MCS = 1011 48 STC rate = 4, MCS = 1100 49 STC rate = 4, MCS = 1101 50 STC rate = 4, MCS = 1110 51 STC rate = 4, MCS = 1111 52 Reserved 53 Reserved 54 Reserved 55 Event-driven Indicator (EDI) for Buffer management Event-driven for buffer management (80% full) 56 Event-driven Indicator (EDI) for Buffer management (full) 57 Event-driven Indicator (EDI) for request for switching Indicate request to switch MIMO MFM feedback Mode between distributed and localized allocations 58 Event driven indicator (EDI) for frequency partition 0 AMS informs ABS about the frequency indication (reuse-1) partition index (for MIMO feedback 59 Event driven indicator (EDI) for frequency partition 1 modes 0, 1, 4, 7) indication (reuse-3) 60 Event driven indicator (EDI) for frequency partition 2 indication (reuse-3) 61 Event driven indicator (EDI) for frequency partition 3 indication (reuse-3) 62 Event-driven Indicator (EDI) for Bandwidth Request Event-driven Indicator for Bandwidth Indicator (sequence 1) request 63 Event-driven Indicator (EDI) for Bandwidth Request Indicator (sequence 2)

According to Table 9, the PFBCH encoding type 0 indicates the STC rate and the modulation and coding scheme (MCS) level of a measured channel.

Table 10 is an example of the PFBCH encoding type 1.

TABLE 10 Index Content (Value) Description/Notes  0 Subband index 0 Subband index for Best-1 subband (refer  1 Subband index 1 15.3.9.3.1.4 feedback format)  2 Subband index 2  3 Subband index 3  4 Subband index 4  5 Subband index 5  6 Subband index 6  7 Subband index 7  8 Subband index 8  9 Subband index 9 10 Subband index 10 11 Subband index 11 12 Reserved Reserved . . . . . . 54 Reserved 55 Event-driven Indicator (EDI) for Buffer management Event-driven for buffer management (80% full) 56 Event-driven Indicator (EDI) for Buffer management (full) 57 Event-driven Indicator (EDI) for request for switching Indicate request to switch MIMO MFM feedback Mode between distributed and localized allocations 58 Event driven indicator (EDI) for frequency partition 0 AMS informs ABS about the frequency indication (reuse-1) partition index (for MIMO feedback 59 Event driven indicator (EDI) for frequency partition 1 modes 0, 1, 4, 7) indication (reuse-3) 60 Event driven indicator (EDI) for frequency partition 2 indication (reuse-3) 61 Event driven indicator (EDI) for frequency partition 3 indication (reuse-3) 62 Event-driven Indicator (EDI) for Bandwidth Request Event-driven Indicator for Bandwidth Indicator (sequence 1) request 63 Event-driven Indicator (EDI) for Bandwidth Request Indicator (sequence 2)

According to Table 10, the PFBCH encoding type 1 indicates the index of a best-1 subband whose narrowband CQI will be measured.

The PFBCH encoding type 2 is used for a PMI report.

FIG. 10 is a block diagram showing a process in which feedback information is mapped to an SFBCH. At step S60, an SFBCH payload is subject to channel coding through convolutional codes. Here, the coding process may vary depending on the length of the payload. At step S61, a quadrature phase shift keying (QPSK) modulation is performed on the channel-coded symbol. At step S62, the modulation symbol and a pilot sequence are combined to form one a symbol sequence. The symbol sequence is mapped to the subcarrier of an FMT.

Meanwhile, when a measurement result for a selected subband (best-M) not all the bands is fed back, the index of the selected subband is also fed back. At least one subband is selected from a predetermined subband set, and a measurement result in the relevant subband and the subband index are fed back. When the subband set is configured or the subband index is fed back, the following factors need to be taken into consideration.

1) The number of subbands included in a bandwidth is varied depending on the bandwidth. A 5 MHz bandwidth includes 6 subbands, a 10 MHz bandwidth includes 12 subbands, and a 20 MHz bandwidth includes 24 subbands. Accordingly, if the same number of subband indices is sought to be fed back irrespective of the bandwidth, the size of the subband set is varied depending on the bandwidth. If the size of the subband set is fixed, the number of subband indices fed back is varied.

2) Since a subband includes 4 contiguous CLRUs, feedback information for the subband including the CLRUs need to be fed back.

3) When a bandwidth is partitioned into a plurality of frequency partitions, transmission power applied to each frequency partition may be different. Accordingly, when a subband is selected or a subband set is determined, the frequency partitions have to be taken into consideration.

Accordingly, the present invention proposes a method of configuring a subband set or feeding a subband index back by taking the above factors into consideration.

FIG. 11 is an embodiment of the proposed feedback transmission method.

At step S100, a UE selects at least one subband among a plurality of subbands forming a subband set. At step S120, the UE transmits feedback information, measured for the at least one subband, to a BS. Here, the feedback information includes the index of the at least one subband. Furthermore, the at least one subband may be selected by taking frequency partitions or the resource mapping of the plurality of subbands into consideration.

When a subband set is configured, one subband may form one subband set. Accordingly, a 5 MHz bandwidth includes 6 subband sets, a 10 MHz bandwidth includes 12 subband sets, and a 20 MHz bandwidth includes 24 subband sets. When a subband index is fed back through a PFBCH, the PFBCH encoding type 1 is used and a current PFBCH encoding type 1 is configured to select any one of 12 subbands. In order to support the 24 subband sets included in the 20 MHz bandwidth, the PFBCH encoding type 1 may be newly configured as in Table 11.

TABLE 11 Index Content (Value) 0 Subband index 0 1 Subband index 1 2 Subband index 2 3 Subband index 3 4 Subband index 4 5 Subband index 5 6 Subband index 6 7 Subband index 7 8 Subband index 8 9 Subband index 9 10 Subband index 10 11 Subband index 11 12 Subband index 12 13 Subband index 13 14 Subband index 14 15 Subband index 15 16 Subband index 16 17 Subband index 17 18 Subband index 18 19 Subband index 19 20 Subband index 20 21 Subband index 21 22 Subband index 22 23 Subband index 23 24 . . .

In Table 11, 0˜5 sequences may be used in the 5 MHz bandwidth. Likewise, 0˜11 sequences may be used in the 10 MHz bandwidth, and 0˜23 sequences may be used in the 20 MHz bandwidth. The UE selects one subband from among 6, 12, or 24 sequences corresponding to the bandwidth of a system, measures feedback information in the relevant subband, and feeds the measured feedback information back together with the index of the relevant subband.

If the number of subbands selected so as to measure the feedback information is 1 or more, a subband index and measured feedback information may be fed back through an SFBCH. Here, the subband index may be fed back using a bitmap scheme. To this end, the number of bits equal to the number of subbands is necessary. That is, among the number of bits equal to a subband set, ‘1’ may be allocated to a bit corresponding to a selected subband, and ‘0’ may be set to a bit corresponding to unselected subbands. For example, assuming that first, third, and seventh subbands are selected in the 10 MHz bandwidth, a bit sequence ‘101000100000’ having a length of 12 is fed back through an SFBCH. Alternatively, in order to reduce signaling overhead, combinations of subbands that may be selected from a subband set may be sequentially arranged and a sequence indicating the combination may be used. In other words, when the number of subband sets is S and the number of selected subbands is M, the number of combinations equal to _(S)C_(M) is possible, and the number of bits ┌log₂ C(S,M)┐ may represent all possible subband combinations may be used. For example, when S=24 and M=3, a combination of selectable subbands is

${{}_{}^{}{}_{}^{}} = {\frac{24 \cdot 23 \cdot 22}{3 \cdot 2 \cdot 1} = 2024.}$

The 2024 subband combinations may be represented by 11 bits, and a subband index selected using the 11 bits may be fed back. Here, the number of necessary bits is changed depending on a bandwidth and the number of selected subbands.

Alternatively, all the bandwidths may be configured to have the same number of subband sets irrespective of the bandwidth. Accordingly, the number of subbands included in one subband set is changed depending on the bandwidth. For example, if the number of all subband sets is 12, one subband set includes 0.5 subband in the 5 MHz bandwidth, 1 subband in the 10 MHz bandwidth, and 2 subbands in the 20 MHz bandwidth. UE may measure feedback information, select at least one of the configured subband sets, and feed feedback information measured for the relevant subband set back. However, if the relevant 2 subbands belong to different frequency partitions when the one subband set includes the 2 subbands in the 20 MHz bandwidth, the feedback information cannot be accurately measured. For this reason, as in the 10 MHz bandwidth, in the 20 MHz bandwidth, one subband set is also configured to include one subband, but a subband may be selected in only 12 subband sets from 24 subband sets. Since pieces of feedback information about contiguous subbands having the same transmission power level within a frequency partition may have a similar value, the total number of subband sets may be set to 12 by configuring subband sets using only a subband set having an odd-numbered or even-numbered index from among the subband sets. Alternatively, feedbacks for the subband set having the even-numbered index or the subband set having the odd-numbered index may be alternately transmitted in the time axis.

Furthermore, if the entire bandwidth is partitioned into a plurality of frequency partitions, feedback information about only subbands belonging to a specific frequency partition may be measured and feedback information about M subbands, selected from among the subbands, may be fed back. Assuming that the number of all subband sets is S and the number of subband sets belonging to a specific frequency partition is P, feedback information about M subbands selected from among the S subband sets may be measured and feedback information about subbands belonging to a specific frequency partition, from among the M selected subbands, may be fed back. Alternatively, feedback information about the P subband set may be measured, and feedback information about the M selected subbands from the P subband set may be fed back. If the M subbands are selected from the P subband set, signaling overhead can be reduced as compared with a case where the M subbands are selected from the S subband set, but there is a disadvantage in that the number of transmitted bits is changed depending on a change of P.

A BS may inform the specific frequency partition from which the M subbands are selected through a feedback allocation A-MAP IE, and UE may directly select the specific frequency partition. If the UE directly selects the specific frequency partition, the UE has to inform the BS of the selected specific frequency partition by using the PFBCH encoding type 0 or 1. In this case, the indices 58˜61 of the PFBCH encoding type 0 or 1 may be used. Table 12 is an example in which the FPI field of the feedback allocation A-MAP IE in Table 1 is reconfigured when the BS informs the UE of the specific frequency partition.

TABLE 12 If(MFM=0,1,4,7){  FPI [2] Frequency partition indication: ABS indicate AMS to send wideband CQI and STC rate of frequency partition and reuse factor in the future: 0b00: Frequency partition index 0 0b01: Frequency partition index 1 0b10: Frequency partition index 2 0b11: Frequency partition index 3 }

That is, a BS may always inform UE of information about a frequency partition that must be measured irrespective of an MIMO feedback mode through a feedback allocation A-MAP IE. The UE transmits wideband feedback information about the relevant frequency partition or narrowband feedback information including the subband index of the relevant frequency partition based on the information about the frequency partition. If a subband belonging to a frequency partition other than the frequency partition that must be measured for a feedback is included in a subband set, only feedback information about the subband belonging to the frequency partition that must be measured for a feedback may be fed back. That is, if the same number of subband sets is configured irrespective of a bandwidth and one subband set includes 2 subbands according to the 20 MHz bandwidth, feedback information may be differently configured depending on the configurations of frequency partitions to which the 2 subbands belong, respectively. For example, if 2 subbands forming a subband set belong to a selected specific frequency partition, UE transmits feedback information measured for both the 2 subbands. If only one subband belongs to the selected specific frequency partition, the UE transmits feedback information about the one subband belonging to the selected specific frequency partition, from among pieces of measured feedback information about the 2 subbands. If both the 2 subbands do not belong to the selected specific frequency partition, the measured feedback information may not be transmitted.

Furthermore, subbands may be mapped in a CLRU or a DLRU. Subbands requiring narrowband feedback information, from among the subbands, are subbands mapped in the CLUR, and wideband feedback information not narrowband feedback information is measured for subbands mapped in the DLRU. Accordingly, feedback information about only the subbands mapped in the CLRU is measured, and feedback information about selected M subbands, from among the subbands, may be fed back. Assuming that the total number of subband sets is S and the number of subband sets mapped in the CLRU is G, feedback information about M selected subbands in the S subband sets may be measured, and feedback information about subbands belonging to subband sets mapped in the CLRU, from among the M selected subbands, may be fed back. Alternatively, feedback information about a G subband set may be measured, and feedback information about M selected subbands in the G subband set may be fed back. If M subbands are selected from the G subband set, signaling overhead can be reduced as compared with a case where the M subbands are selected from the S subband set, but there is a disadvantage in that the number of transmitted bits is changed according to a change of G. If the subband mapped in the CLRU and the subband mapped in the DLRU coexist in a subband set, only feedback information about the subband mapped in the CLRU, requiring feedback measurement, may be measured and fed back.

Alternatively, the proposed inventions may be combined and applied. For example, in selecting subbands from a subband set belonging to a specific frequency partition, only subbands mapped in the CLRU may be selected. On the other hand, in selecting subbands from subband set mapped in the CLRU, only subbands belonging to a specific frequency partition may be selected.

FIG. 12 is a block diagram showing a BS and UE in which the embodiments of the present invention are implemented.

The BS 800 includes a processor 810, memory 820, and a Radio Frequency (RF) unit 830. The processor 810 implements the proposed functions, processes, and/or methods. The processor 810 processes a feedback allocation A-MAP IE. The layers of a radio interface protocol may be implemented by the processor 810. The memory 820 is coupled to the processor 810, and it stores various pieces of information for driving the processor 810. The RF unit 830 is coupled to the processor 810, and it transmits and/or receives radio signals and transmits the feedback allocation A-MAP IE.

The UE 900 includes a processor 910, memory 920, and an RF unit 930. The processor 910 implements the proposed functions, processes, and/or methods. The processor 910 selects the at least one subband from among a plurality of subbands forming a subband set. The feedback information includes the index of the at least one subband, and the at least one subband may be selected by taking the frequency partition or resource mapping of the plurality of subbands into consideration. The proposed feedback transmission methods may be implemented by the UE of FIG. 12. Furthermore, the layers of a radio interface protocol may be implemented by the processor 910. The RF unit 930 is coupled to the processor 910, and it transmits feedback information measured for the at least one subband. The memory 920 is coupled to the processor 910, and it stores various pieces of information for driving the processor 910.

The processors 810, 910 may include application-specific integrated circuit (ASIC), other chipset, logic circuit and/or data processing device. The memories 820, 920 may include read-only memory (ROM), random access memory (RAM), flash memory, memory card, storage medium and/or other storage device. The RF units 830, 930 may include baseband circuitry to process radio frequency signals. When the embodiments are implemented in software, the techniques described herein can be implemented with modules (e.g., procedures, functions, and so on) that perform the functions described herein. The modules can be stored in memories 820, 920 and executed by processors 810, 910. The memories 820, 920 can be implemented within the processors 810, 910 or external to the processors 810, 910 in which case those can be communicatively coupled to the processors 810, 910 via various means as is known in the art.

In view of the exemplary systems described herein, methodologies that may be implemented in accordance with the disclosed subject matter have been described with reference to several flow diagrams. While for purposed of simplicity, the methodologies are shown and described as a series of steps or blocks, it is to be understood and appreciated that the claimed subject matter is not limited by the order of the steps or blocks, as some steps may occur in different orders or concurrently with other steps from what is depicted and described herein. Moreover, one skilled in the art would understand that the steps illustrated in the flow diagram are not exclusive and other steps may be included or one or more of the steps in the example flow diagram may be deleted without affecting the scope and spirit of the present disclosure.

What has been described above includes examples of the various aspects. It is, of course, not possible to describe every conceivable combination of components or methodologies for purposes of describing the various aspects, but one of ordinary skill in the art may recognize that many further combinations and permutations are possible. Accordingly, the subject specification is intended to embrace all such alternations, modifications and variations that fall within the spirit and scope of the appended claims. 

1. A method of transmitting a feedback in a wireless communication system, the method comprising: selecting at least one subband among a plurality of subbands forming a subband set; and transmitting feedback information measured for the at least one subband, wherein the feedback information comprises an index of the at least one subband, and the at least one subband is selected by taking a frequency partition or a resource mapping of the plurality of subbands into consideration.
 2. The method of claim 1, wherein: the at least one subband is selected from all subband sets, and the at least one subband belongs to a selected specific frequency partition.
 3. The method of claim 2, wherein information about the specific frequency partition is signalized by a feedback allocation advanced-MAP (A-MAP) information element (IE).
 4. The method of claim 2, wherein the specific frequency partition is selected by a user equipment.
 5. The method of claim 4, wherein information about the specific frequency partition is fed back to a base station according to a primary fast feedback channel (PFBCH) encoding type
 1. 6. The method of claim 1, wherein the at least one subband is selected from the subband set belonging to a specific frequency partition.
 7. The method of claim 1, wherein: the at least one subband is selected from all subband sets, and the at least one subband belongs to a subband set mapped in a contiguous logical resource unit (CLRU).
 8. The method of claim 1, wherein the at least one subband is selected from a subband set mapped in the CLRU.
 9. The method of claim 1, wherein the feedback information is transmitted to a base station through a PFBCH or a second fast feedback channel (SFBCH).
 10. An apparatus for transmitting a feedback in a wireless communication system, the apparatus comprising: a radio frequency (RF) unit configured for transmitting feedback information measured for at least one subband; and a processor, coupled to the RF unit, configured for selecting the at least one subband from among a plurality of subbands forming a subband set, wherein the feedback information comprises an index of the at least one subband, and the at least one subband is selected by taking a frequency partition or a resource mapping of the plurality of subbands into consideration.
 11. The apparatus of claim 10, wherein: the at least one subband is selected from all subband sets, and the at least one subband belongs to a selected specific frequency partition.
 12. The apparatus of claim 10, wherein the at least one subband is selected from the subband set belonging to a specific frequency partition.
 13. The apparatus of claim 10, wherein: the at least one subband is selected from all subband sets, and the at least one subband belongs to a subband set mapped in a contiguous logical resource unit (CLRU).
 14. The apparatus of claim 10, wherein the at least one subband is selected from a subband set mapped in the CLRU.
 15. The apparatus of claim 10, wherein the feedback information is transmitted to a base station through a primary fast feedback channel (PFBCH) or a second fast feedback channel (SFBCH). 